QUIC Transport Protocol

RFC 9000 defines QUIC, a secure, general-purpose, multiplexed transport protocol operating directly on top of UDP.

Core Features

Authenticated & Encrypted: All packet headers and payloads are encrypted using TLS 1.3 (RFC 9001). Middleboxes and firewalls cannot inspect or tamper with stream headers.
Stream Multiplexing: Unidirectional and bidirectional streams with per-stream and connection flow control, RESET_STREAM/STOP_SENDING, and MAX_STREAMS updates.
Low Latency Handshake: 1-RTT connection setup and 0-RTT resumption with PSK tickets, bounded server-side anti-replay, and early-data policy enforcement.
Recovery & Congestion Control: ACK tracking, RTT estimation, PTO probes, loss declaration/retransmission, and a NewReno controller are integrated into the send/receive paths.
Transport Parameters: Peer parameters are exchanged during the handshake and applied to stream limits and flow-control windows.
Handshake Lifecycle: The server confirms after verifying the client Finished and signals HANDSHAKE_DONE; the client confirms on that frame or on an acknowledgment of a 1-RTT packet. Confirmation discards the Handshake keys and releases their recovery state, and late Handshake packets are ignored (RFC 9001 Sections 4.1.2 and 4.9.2).

Retry/token validation, QUIC v1/v2 version negotiation, and 1-RTT key updates are implemented; compatible-version negotiation is not.
No HelloRetryRequest handling in the QUIC TLS driver.
No connection migration yet.
The high-level HTTP/3 client pools QUIC connections for sequential reuse without multiplexing concurrent requests over one connection; the server multiplexes requests on its active connection.

Initial: Initiates connection and carries TLS ClientHello / ServerHello.
Handshake: Completes mutual authentication and exchanges application keys.
0-RTT Protected: Carries early application data for resumed sessions.
1-RTT (Short Header): Carries standard application streams with minimum 1-byte header overhead.